Planted Tank Enthusiast
Join Date: Oct 2004
Location: surf city, cali
well, there are many variables at play in the notional calculation, that i wouldn't necessarily take it as an absolute value. what is important to note is that
a) silicone is generally a poor choice for high pressure CO2 transport since it's widely known to have high permeability,
b) keep the runs of tubing as short as possible, and
c) thicker walled tubing helps reduce losses
also, i imagine the CO2 setup has a lot to do with it, since it affects the partial pressure gradient. a setup using a ceramic disc / glass diffuser with a very low bubble rate at a fairly high constant pressure is going to have a much different net flux than someone feeding the inlet of a CO2 reactor at low pressure where the CO2 is being 'sucked' in from venturi effects. in the later case, silicone might work great.
note that the silicone tubing from drs fosters and smith is 1/8" ID versus 3/16" ID, with possibly greater wall thickness too?. so, the net flux for the 1/8" ID should be 2/3 that of the 3/16" ID at the very least.
lastly, i'm not sure 'silicone is silicone is ...', so the properties of the one offered at drs fosters and smith may be different than the ones from cole-parmer.
like you said, there are LOTS of other choices of tubing which are an order of magnitude or more better for CO2 permeability than silicone.